This invention relates to a method for coating ceramic discs, using said discs in fluids mixer valves of the single-lever mixer type.
This invention also relates to a ceramic disc obtained by said method and which thus permits a reduction of the friction coefficient between the coated ceramic discs.
Mixer valves of the single-lever type include a pair of ceramic discs mounted one on top of the other. The rotation of the upper disc on the lower disc, which is fixed, determines the mixture of cold and hot water, permitting in its end positions the output of only cold water or only hot water. The diametral sliding of the upper disc on the lower disc determines the opening and closing of the valve, permitting the output flow of water to be adjusted.
One problem these ceramic discs have is that a low friction coefficient must be combined with excellent leak tightness. For this reason, it is usual to use grease to reduce the friction coefficient, though no kind of coating adhering to the discs is used.
An attempt has been made to solve these disadvantages by using hydrogenated amorphous carbon, usually known as DLC (Diamond-Like Carbon) to reduce the friction coefficient. This compound, also defined as amorphous diamond, is a combination of various carbon structures (graphite, diamond, amorphous carbon, etc.).
WO/860458 discloses a method for manufacturing members for seals, such as ceramic discs, for controlling the flow of fluids in a valve. Said seals are made of ceramics, metal or synthetic materials. These seals are coated with a fine layer of a hard material such as silicon carbide, metal carbide, metal nitrides or cubic crystalline carbon. The coating can be implemented by chemical vapour deposition (CVD). This method permits functioning of the valves without need for lubricant.
U.S. Pat. No. 5,927,727 discloses seal members, especially for sealing and regulating devices, together with a method for manufacturing them. Said members can be made of metallic or non-metallic materials, such as a ceramic material like Al2O3 SiC, Si2C or Si3N4.
These valves include a coating of multiple layers, a coat of silicon with low carbon content in order to improve adherence and increase hardness, and a second coat of carbon with silicon in order to reduce the friction coefficient. Once the valve with the coating has been obtained it is submitted to a curing process for 30 to 60 minutes at 500xc2x0 C., or of 30 seconds to 1 minute at 900xc2x0 C. The deposition is carried out by chemical vapour deposition or polymerisation by plasma.
U.S. Pat. No. 5,100,565 discloses a valve made up of a fixed disc and a sliding ceramic disc. These discs present a coating of DLC deposited by means of chemical vapour deposition by plasma. The objective of these valves is to ensure that the discs function correctly with coating and without grease. In order to improve adherence of the coating, multiple layers of TiN, TiC and DLC are deposited.
EP-0 884 509 discloses the use of ceramic discs for valves coated with DLC with an intermediate layer of titanium and silicon in order to achieve correct functioning and longer valve life. The deposition method is chemical vapour deposition by plasma, in which the reactive gases are TiCl4, SiCl4 and C6H6.
Although all the documents cited relate to coating of valves and ceramic or metal seals in order to achieve hardness and a low friction coefficient without need for lubricants, it is always necessary to deposit at least one intermediate layer, in order to improve adherence and achieve greater hardness. That is, none of the documents cited describe the deposition of DLC directly onto the ceramic members.
Another disadvantage of the methods disclosed in the documents cited is that the deposition process is carried out at high temperatures, mainly between 700xc2x0 C. and 900xc2x0 C., and in the case of depositions at high temperature curing is needed after the deposition, and this entails a high manufacturing cost.
The method and the disc of this invention manage to resolve the aforesaid disadvantages, while presenting other advantages which will be described below.
The method of this invention for the coating of previously lapped and polished ceramic discs is characterized in that it includes the phases of:
preparation of said ceramic discs; and
deposition of a layer of hydrogenated amorphous carbon on said ceramic discs;
with said deposition phase including the following stages:
exposure of said ceramic discs to a vacuum;
application of a cleaning plasma on said ceramic discs;
application of a first deposition plasma on said ceramic discs; and
application of a second deposition plasma on said ceramic discs.
Advantageously, said deposition is carried out by chemical vapour deposition assisted by radio frequency plasma at room temperature.
According to a preferred embodiment, said cleaning plasma is applied by means of argon, at a pressure between 8 and 12 Pa, with an auto polarization power of between xe2x88x921000 and xe2x88x92600 V and for a period of time of between 4 and 10 minutes.
Preferably, said first deposition plasma is applied by means of methane, at a pressure between 8 and 12 Pa, with an auto polarization power of between xe2x88x92400 and xe2x88x921000 V, with a radio frequency power between 250 and 275 W, and for a period of time of between 2 and 5 minutes.
According to said preferred embodiment, the second deposition plasma is applied by means of methane, at a pressure between 8 and 12 Pa, with an auto polarization power of between xe2x88x92300 and xe2x88x92700 V, with a radio frequency power between 40 and 60 W, and for a period of time of between 5 and 9 minutes.
Said phase of preparation of the ceramic discs includes, preferably, the following phases:
cleaning of the ceramic discs;
drying of said ceramic discs; and
evaporation of substances impregnated in said ceramic discs.
Said cleaning of the ceramic discs can be carried out by means of acetone and ethanol baths in an ultrasound washer for a period of time between 15 and 25 minutes.
According to a second embodiment, the invention also relates to a ceramic disc which is applicable to fluid mixer valves, characterized in that it includes a layer of hydrogenated amorphous carbon deposited directly onto the ceramic disc.
Said layer of hydrogenated amorphous carbon has a thickness of between 275 and 325 nm and a hardness of between 10 and 18 GPa.
The coating method of this invention achieves ceramic discs for utilization in mixer valves of the single-lever type whose friction coefficient is lower than that of the ceramic discs currently used, all this without loss of leak tightness, without having to use greases or intermediate layers and with a reduced manufacturing cost, thanks to the speed of the process and the carrying out of the deposition at room temperature.